In a conventional method of modifying a metal oxide film formed on a surface of a substrate by using a modifying gas generated by exciting an O2 gas by plasma, a method of modifying a metal oxide film by setting a temperature of a substrate during modification to a temperature ranging from room temperature to a temperature lower than a temperature at which the metal oxide film is crystallized, and then crystallizing the metal oxide film as necessary has been known.
Further, a method of modifying a metal oxide film by setting a temperature of a substrate during modification to a temperature higher than a temperature at which the metal oxide film is crystallized to thereby simultaneously perform modification and crystallization has also been disclosed.
However, the purpose of film formation is not limited to the formation of an electronic circuit, and film formation may be performed to manufacture a hard mask for forming a pattern. In this case, a technology of forming a film with a smooth surface having low surface roughness, rather than a film having a rough surface due to crystallization is required.